Antenna amplifier

ABSTRACT

An antenna amplifier utilizes integrated dual duplex filters having a first filter branch for allowing through a transmitter band (Tx) between an uplead and an antenna, a second filter branch (Rx1) for allowing through a receiver band (Rx) from the antenna to an output element (3), a third filter branch for allowing through the receiving band (Rx) from an input element (4) to the uplead, and a low noise amplifier whose input is connected to the output element and whose output is connected to the input element. The low noise amplifier (LNA) is preferably both constructed and connected by means of filter-technical and circuit board-technical methods.

FIELD OF THE INVENTION

The invention relates to an antenna amplifier.

DESCRIPTION OF THE BACKGROUND ART

In mobile communication systems, it is normal for a fixed station totransmit within a given frequency range and to receive within afrequency range that differs from the transmitting range. In certainapplications, both transmission and reception are effected with the sameantennas. The reason for this is to be found in the general desire tooperate from a base station in a mobile communications tower in an areathat is divided into separate sectors while utilizing diversity. The useof separate antennas for transmission and reception would result in anexcessively large number of antennas.

In view of the relatively long downleads that are involved in thisregard, there is an interest in amplifying the received signals alreadyin connection with and close to the antenna, particularly in the case offixed tower-mounted stations. In this regard, it is necessary tomutually separate the received incoming signals with the aid of filters,which must have the highest quality in order to bring losses down to aminimum. In an earlier known construction, the transmitter signal hasbeen separated from the receiver signal with the aid of two signalpaths, one for the transmitter signal and one for the receiver signal,each of which is connected to respective antenna and uplead sidesthrough a duplex filter. Each duplex filter is comprised of two filterstuned to respective transmission and reception frequency bands. Theadvantage with this construction is that only one downlead to the groundmounted station is required. However, it can also be chosen to upleadthe transmission power and downlead the receiver signal in a respectivecoaxial cable, thereby enabling a saving in ground positioned filterstages.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved antennaamplifier. Among other things, it is desired to therewith improve theisolation or separation between transmitter and the receiver bands,therewith to reduce losses in the transmission bands and to reducenon-linearity in the transmitter band, and also to reduce the occurrenceof spurious intermodulation products and to obtain the least possiblereception noise factors and the most effective transmission emission andalso to achieve low weight and small size.

Such advantages are achieved in accordance with the invention with anantenna amplifier of the kind defined below.

According to one embodiment of the invention, there is provided anantenna amplifier which includes sequentially in a row a first receptionband filter, a transmission band filter and a second receiver bandfilter, said filters being built-up in a comb-line structure. Anamplifier-connected output and input are provided at respective ends ofthe row. Coupling means are placed on both sides of the midwaytransmitter band filter for connection to an antenna and to a downleadto a fixed station. Also included is an arrangement in which the firstand the second receiver band filter are placed side by side-in arespective cavity with the transmitter band filter mounted perpendicularthereto in a separate cavity, wherein the connection therebetween iseffected via apertures and inputting first resonators.

An antenna amplifier of the kind in question is meant to be mounted in atower, which may have a height of 60 meters, where servicing is effectedby service personnel climbing a ladder and working outdoors.Accordingly, an object of the present invention is to provide anamplifier of the aforesaid kind which can be readily handled, easilyreplaced and which is effective in operation. It shall also be possibleto mass-produce the antenna amplifier at reasonable cost, in view of thelarge number of amplifiers required to expand or extend mobile telephonytraffic. The amplifier shall be easy to connect-up, insensitive, and assmall and as light as possible.

An important aspect in this regard resides in the desire to fullyutilize the possibilities that are afforded by integrated circuits whenthey can be connected directly to the filter devices without requiring,for instance, coaxial coupling devices and while maintaining couplinglosses and distortion at the smallest possible levels.

These objects are achieved in accordance with the invention with anantenna amplifier of the kind set forth below.

Two essential features in genuine combination are contributory in thisregard: The construction of a comb-line filter connected via connectorpins for its inputs and outputs and accommodated in a folded cavity ofhorseshoe configuration cavity defined by a metal casing, and a circuitboard mounted amplifier with the input adaptively connected to thefilter via a connector pin incoming to the circuit board at rightangles. This construction provides on the input an excellent low-lossconnection, particularly in comparison with a connection made to aseparate amplifier via a coaxial connection. The combination iscompleted by mounting the circuit board in a rigid metal constructionthat accommodates the actual filter.

The inventive combination can be utilized either with a combinationhaving a common uplead and downlead, or with separate upleads anddownleads. In the former case, a filter is not only required toseparate-out the receiver signal, but also to pass the amplifiedreceiver signal to the common uplead and downlead.

With regard to the combination that includes a common uplead anddownlead, there is provided in accordance with one variant a filterdevice in which two parallel filters have inputs which lie close to oneanother and which are also mutually connected to another filter withoutthe need of hybridizing between Coax Cavity and Comb-line. It has beenfound that the invention enables the three filters and the aforesaid twoinput/outputs to be connected to a single cavity that has two mutuallyparallel straight parts which are bridged by a curved part thataccommodates the center filter.

Among the improvements desired are the isolation between the transmitterand receiver bands, reduction in losses in the Tx path and a reductionin the non-linearity in the transmitter band, which is dedicated towardsreducing the occurrence of spurious intermodulation products, to achievethe smallest possible noise factor for the reception and the maximumpossible effective emission for the transmitter, in addition to lowweight and small size.

The actual amplifier is mounted on a circuit board placed adjacent thecavity, and connections are made through pin connectors, either directlywith inductive coupling or with capacitive coupling to circuit boardconductors of the microstrip or stripline type and with appropriateinpedance match.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to anon-limiting exemplifying embodiment thereof and also with reference tothe accompanying drawings, in which

FIG. 1 is a schematic diagram illustrating an antenna amplifier forduplex operation in accordance with an earlier known technique;

FIG. 2 is a schematic diagram illustrating an antenna amplifierconstructed in accordance with the principles of the invention;

FIG. 3 presents schematic views of one embodiment of an inventive filtercombination;

FIG. 4 illustrates an advantageous embodiment of a filter combination;

FIG. 5 illustrates one type of amplifier coupling with low losses;

FIG. 6 illustrates an advantageous bypass coupling means of an amplifierunit:

FIGS. 7A, B and 8A, B show a frequency curve relating to a factualdesign of the embodiment illustrated in FIG. 3;

FIG. 9 illustrates schematically a folded dual duplex filter inaccordance with the principles of the present invention;

FIGS. 10A, 10B and 11 are perspective views of a filter construction;

FIGS. 12A-C are drawings of one example of a dual duplex filter on whichmeasurements have been inserted:

FIGS. 13 and 14 illustrate examples of inductive circuit boardinputting;

FIGS. 15A, B and 16A, B are diagrams showing frequency curves foradjusted examples of the embodiment shown in FIGS. 12A-C, with adisconnected amplifier and with an amplifier functioning for signalsincoming from the antenna side respectively;

FIGS. 17A, B and 18A, B are diagrams showing adaptation curves andtransmission curves respectively for the same embodiment;

FIG. 19 is a partially exploded view showing the general construction ofanother embodiment of the invention; and

In mobile communication systems, the frequency bands normally lie at1,700-1,900 MHz and at 800-1,000 MHz respectively. The radio channelspacing between transmitter and receiver bands is normally 20 MHz. Thisconcerns frequency ranges suitable for the application of microwavetechnology.

FIG. 1 illustrates schematically a known antenna amplifier connectedbetween an antenna and an uplead (Tower Mounted low noise Amplifier,TMA). There are obtained with the aid of two duplex filters twoconductor branches, one branch Tx for the transmitter signal and anotherbranch Rx for the received signal, it being possible to mutuallyseparate the signals through filters by virtue of the signals lying indifferent frequency bands. Such broadband filters may be comprised ofresonators having slightly different tuning frequencies in comb-linefilters. It will be evident that four such filters are included in thisconfiguration, namely one bandpass filter for the Tx frequency band andone bandpass filter for the Rx frequency band in each duplexer. The lownoise amplifier LNA is connected in the Rx branch.

In accordance with the invention, which is a combination of two duplexfilters having a common Tx filter in one and the same construction, oneof four filters is now eliminated in accordance with the FIG. 2illustration. The transceiver connection BTS is therewith able todeliver transmitter power to the antenna solely via Tx, tuned to itsfrequency band. The signal received by the antenna can only reach theinput on the low noise amplifier LNA via Rx1, the output signal of LNApassing to BTS via the filter Rx2.

A comparison with FIG. 1 shows that in addition to eliminating onefilter, the number of connection points in the Tx path is reduced fromfour to two. With regard to the Tx path, the connection losses arehalved in principle. This results in an improvement in ERP (EffectiveRadiative Power).

It is also possible to integrate filter and amplifier, meaning that theamplifier is connected directly to the filter without requiring cablesand cable connections. This can be achieved with a combination of filtertechnology and circuit board technology (stripline or microstrip).Contact and cable losses upstream of the LNA input are eliminated andlower noise factors are achieved.

Description of a First Embodiment

A specific embodiment of a filter combination of the aforesaid kind isshown in FIG. 3, in which measurements have been inserted inmillimeters. Part-Figures A, B and C are respective views of the upperside, inside and underside of an internally silvered box havingconnections 1, 2, 3, 4 with intermediate filters Rx1, Tx and Rx2respectively. This arrangement is a so-called comb-line structure havingthree resonators 30 which define the Tx pass band and five resonators 31for the Rx pass band. Steepness in the Rx pass band is further increasedby notch filters N at the outermost extremities. Fine adjustments to theresonators are made with the aid of adjuster screws 32, shownschematically in view C. As will be realized by the skilled person, thefilter combination appears as a closed right-angled box with coaxialcontacts projecting out from the surface A and adjuster devices from theopposite surface C.

In one advantageous embodiment, the coaxial connections 1 and 4 can bereplaced with recesses adapted for connection to striplines or the likemounted on a low noise amplifier board placed on the outside of the box(not shown).

The filter box may be of moderate length with regard to frequencieswithin the frequency band 1700-1900 MHz. In the case of frequency bandsbetween 800-1000 MHz, however, the length of the construction will beroughly twice as large and will well exceed one meter. It is thereforeof interest to be able to fold the construction to obtain a shorterlength. The connections 3 and 4 would then be closer together, whichwould further facilitate their connection to one and the same low noiseamplifier board.

Description of a Second Embodiment

The aforesaid basic concept has been developed to produce the filtercombination shown in FIG. 4, this combination having the form of ahybrid between a Coax Cavity and a Comb-line. The antenna andtransceiver coupling or inputting elements are arranged in a cavitytogether with the Tx filter, whereas the Rx filters are each mounted ina respective parallel cavity, wherein inputting to these couplingelements 1 and 2 is effected via apertures and inputting firstresonators. The coupling elements 3 and 4 at opposite ends of thecavities are now located at a comfortable distance apart, whichfacilitates integrated capacitive coupling of a circuit-board mountedlow-noise amplifier, with the high adaptive precision, etc., possiblewith this technique, as illustrated schematically in FIG. 5. Thisconnection setup minimizes losses and enables an optimized low noisefactor to be obtained with respect to the receiving band Rx.

As mentioned in the introduction, the mutual isolation or separation ofthe frequency bands Tx and Rx is one of the important factors. This canbe achieved in principle either with the aid of filters that have a highpole number, which is combined with correspondingly high losses however,or with fewer poles and the inclusion of extra zero poles. Accordingly,in the constructions shown in FIGS. 3 and 4, there have been inserted inthe coupling elements 3 and 4 notches N which function as narrow-bandband stop filters which are tuned to a tangential frequency between theRx and the Tx bands. Because these elements are loss-free in respectivepass bands, filter losses, if any, will be minimized.

As before mentioned, the function of the coupling or inputting elements3 and 4 is to couple the signal between LNA and Rx filters, althoughthey are also used to connect-up the notches N at the same time. Anotherimportant advantage afforded by this type of coupling element is thatthe third order intermodulation products (IM3) are minimized. IM3 is ameasurement of the linearity of the unit.

Because the low noise amplifier is a device that has active components,it may very well break down. In order to ensure that the system willfunction nevertheless, it is known to provide a facility in which theamplifier can be by-passed through a system of coaxial relay contacts.This solution is expensive, however, and is not absolutely reliable.Consequently, in accordance with a preferred embodiment, an activeby-pass is provided adjacent a low noise amplifier mounted on a circuitboard using to this end forwardly biassed diodes as shown in FIGS. 5 and6. Elimination of the forward bias on the diodes will bring the diodesto a high ohmic state and result in coupling-in the by-pass.

When all of the diodes in FIG. 6 are low ohmic, D2 will cause the pointC to be short-circuited to earth. The quarter wavelength conductortransforms this short circuit to an open conductor in point B. The sameapplies to D3 in point G. The conductor that joins the diodes D2 and D3therewith has a negligible influence. D1 results in a short circuit atD, which is transformed to an open conductor in point A, which in turnresults in transformation to a short circuit in point B (the sameapplies to the diode D4 and the point G). The signal will therewith passthrough LNA. In the event of a fault, the bias on the diodes is chokedso as to bring the diodes to a high ohmic state. D2 and D3 will nottherewith influence the by-pass line, and because D1 brings about anopen line in point B the signal will proceed via the by-pass line. Thiscoupling results in minimum losses when the by-pass line isdisconnected, particularly when compared with conventional switchingdevices provided with relay contacts, which are also complicated andextremely expensive in comparison with the cost entailed by the fourdiodes on a circuit board.

EXAMPLE

A filter having the configuration shown in FIG. 2 was constructed withthree resonators in the Tx part and six resonators in the Rx parts. Theintended frequency band limits 1,850-1,875 GHz for Tx and 1,755-1,780GHz for Rx. FIGS. 7A, B and FIGS. 8A, B show filter curves for Tx andfor one of the Rx filters respectively. The A-curves show terminaladaptation and the B-curves show filter transmission. It will be seenfrom FIG. 8B that the relative attenuation for Tx is above 90 dB inrelation to Rx transmission. FIG. 7B shows that the Rx attenuation inrelation to the Tx transmission in the Tx band filter exceeds 40 dB. Itis therefore possible to achieve a very high degree of separation atparticularly low losses in the Tx band (typically 0.2 dB).

Description of a Third Embodiment

As before mentioned, an interest has been shown in the ability to foldthe filter box in order to obtain a shorter length. The connections 3and 4 for the amplifier LNA will then be located closer together, whichfacilitate their connection to one and the same circuit board.

The fundamental concept of the invention has been developed to producethe filter combination shown in FIG. 9. The antenna and transceivercoupling or inputting elements are arranged together with the Tx filterin a curved part of the cavity, whereas the Rx filters are each mountedin respective mutually parallel straight parts of the same cavity, saidstraight parts forming extensions on both sides of the curved part,which describe an arc of 180°.

The coupling elements to transmitter and antenna are placedapproximately at the ends of the bend. The coupling elements 3 and 4 atthe opposite ends of the cavities are now spaced at a comfortabledistance apart, which facilitates integrated coupling of an amplifier ona circuit board mounted outside the filter construction.

The construction of comb-line filters of the kind to which the inventionrefers is largely impossible to calculate by analytic processing. Theconstruction is therefore conveniently effected by computer simulation.Generally speaking, the construction is commenced by determiningcoupling coefficients, i.e. the distances between the successiveresonance circuits, by making trial runs and interative calculations, inorder to obtain an appropriate bandwidth. This establishes themechanical construction. Adjustment to the filters is then effected withthe aid of a network analyzer.

As mentioned in the introduction, the isolation between the frequencybands Tx and Rx is one of the important factors. This can be achieved inprinciple either with the aid of filters that have a high pole number,which is accompanied by corresponding high losses, however, or by using,fewer poles and including extra zero poles. Consequently, in theconstruction shown in FIG. 9, there have been inserted adjacent thecoupling elements 3 and 4 notches N which function as narrow-band bandstop filters tuned to a tangential frequency between the Rx and the Txbands. This enhances steepness and separation. Because these elementsare loss-free in respective pass-bands, the filter losses are minimized.

As before mentioned, the coupling or inputting elements 3 and 4 functionto switch the signal between LNA and Rx filter but are used at the sametime to input the notches N. Another important advantage afforded bythis type of coupling or inputting element is that third orderintermodulation products (IM3) are minimized.

FIG. 10A is a perspective view of an opened filter in accordance withthe invention, and FIG. 10B illustrates its removed lid or cover fromthe inside. FIG. 11 illustrates the "underside" (not seen in FIG. 10A)with a circuit board having a partially exposed, schematicallyillustrated amplifying circuit. The curved cavity measuring 21×36 mm incross-section, is accommodated in solid aluminium and silvered on itssurface. As with earlier illustrations, the antenna and BTS connectionsare referenced 1 and 2 and are made with coaxial contacts 1' and 2'while matching to 50 ohms via bent pins which enter the cavity and whenthe lid is applied are screwed electrically and mechanically to the lidvia holes 1" and 2" respectively. Upstanding from the bottom of thecavity in FIG. 10A are posts 10 for Tx and 11 for Rx which function asinductances of the resonances, trimming screws 12 incoming from the lidand forming controllable capacitances for the resonance circuits withthe upper surfaces of the posts. The notches N also have capacitydetermining screws 12 (partially hidden FIG. 10B). The connections 3 and4 (FIG. 9) are arranged through posts 13 mounted in the lid (FIG. 10B)and exiting through holes in the bottom (FIG. 10A) to circuit boardconnections 14, to which they are soldered. FIGS. 10A and 10B illustratethe device prior to this manufacturing stage.

These solder points 14 are shown in FIG. 11, on the right side of thecircuit board 20. The circuit board 20 is made of a plastic materialthat has low losses and is provided on the underside with an earth plane(not shown) which enables the construction of circuits in microstrip andthe connections to be connected directly to the filter inputs andoutputs intended for the amplifier LNA. This connection is shown inFIGS. 12 and 13. The ends of the posts 13 are narrowed at 15 andinserted through a hole that extends through the circuit board 20 (andthrough the earth plane), and are connected on the other side of theboard to a microstrip conductor 21 by means of a respective solder join14. This arrangement enables a matching to 50 ohms to be made, and anyphase error that may occur can be regulated with a surrounding earth pad22 (shown in FIG. 14) and a capacitor (not shown). The amplifier LNA hasnot been shown explicitly on the circuit board illustrated in FIG. 11,but is indicated solely by broken line symbols in view of the fact thatan amplifier of this kind is known to the skilled person. Although theillustrated connection between filter and amplifying circuit is aninductive connection, the connection may alternatively be a capacitiveconnection.

EXAMPLE

A specific embodiment of a filter combination of the aforesaid kind isillustrated in FIGS. 12A-C in which measurements in millimeters havebeen inserted and which show views of the arrangement shown in FIGS.10A, 10B and 11 and from which the complete measurements of anembodiment can be obtained.

Thus, there was constructed a filter having the configuration shown inFIG. 9, although in this case with three resonators in the Tx part andsix resonators in the Rx parts. The intended frequency band limits were1,850-1,875 GHz for Tx, and 1,755-1,780 GHz for Rx. FIGS. 15A, B and16A, B respectively show the performances of the amplifier construction.The A-curves show terminal matching and the B-curves show thetransmission characteristics of TMA.

It will be particularly noted in FIG. 16B that signals in the receiverband have been amplified by slightly more than 12 dB. FIG. 15B showsthat the construction will not be damaged should the amplifier functionfail, because the signals will pass undisturbed through the filterconstruction.

FIGS. 17A and B and FIGS. 18A and B show filter curves for one of the Rxand Tx paths respectively The A-curves show terminal matching. The curvein FIG. 17B shows the transmission between connections 1 and 3 (which isthe same as the transmission between 2 and 4, which is not thereforeshown), whereas FIG. 18B shows the transmission between connections 1and 2. The curves show that very high attenuation values are obtained.

The amplifier is a low noise amplifier constructed on a circuit boardwith the high precision in matching, etc., possible in this technology.This coupling or connection minimizes the losses and can result in anoptimized low noise factor for the receiver band Rx.

As mentioned in the introduction, the invention can also be applied whenseparate upleads are used for transmitter power output and downleads forthe received signals. One such construction is shown schematically inFIG. 19. To provide a better understanding, only a bottom surface 30with resonator pins 11 and notch pins N of the filter accommodatingcavity have been shown, together with an adjacent lid or cover 31. Theconnector pins 1 and 2 input the transmitter power output to the antennathrough the filter located therebetween. The received signal arrivingfrom the antenna passes via the curved filter provided with sixresonator poles to the output pin 13 which outputs the signal to theamplifier mounted on the circuit board 20 in the same way as that in theFIG. 13 and 14 embodiment. FIG. 20 clearly shows how this adapted outputis applied to a standard coaxial contact. The lid includes screws 32which are screwed into the input pins 1, 2 and 13 when assembling thedevice. The lid is, of course, also screwed firmly to the walls (notshown) of the cavity, which similar to the first described embodiment ismilled from a piece of aluminium and silvered internally. Each resonatorpin 11 is completed in the lid by a trimming screw 12, which is screwedin through an opposing hole and locked by a lock nut 33. Although onlyone such setup has been shown, it will be understood that a similarsetup is provided for each resonator and one for each notch resonator N.

There is obtained in this way a particularly practical monolithic devicewhich has a manageable length by virtue of the curvedhorseshoe-configuration of the filter construction. As shown, it ispossible to place all three connections in a row on one and the sameside as coaxial contacts with a mutual spacing which affords comfortableconnection and disconnection of coaxial cables.

We claim:
 1. An antenna amplifier comprising:an antenna connection; atransmitter connection connected to said antenna connection via a firstbandpass filter for transmitter frequencies; a receiver frequencyamplifier comprising an output for connection to a receiver and areceiver frequency amplifier input connected to said antenna connectionvia a second bandpass filter; said first and second bandpass filtersbeing mounted in a common, elongated cavity and including comb-line-typeresonators arranged generally in rows along a cavity mean line; andconnection pins at each of two mutually approaching ends of said firstand second bandpass filters and at each of two outer ends of saidantenna amplifier.
 2. An antenna amplifier according to claim 1, whereinthe low noise amplifier input and output are inputted to respectivefilters via capacitive connections to respective input elements intendedto this end.
 3. An antenna amplifier according to claim 1, furthercomprising notch resonators provided adjacent the input elementsintended for inputting or coupling the low noise amplifier, wherein thenotch resonators function as narrow-band band stop filters tuned to afrequency outside the pass band for the frequency band but lying closethereto on that side thereof closest to the first frequency band, byoccasioning enhanced isolation between the bands with minimal filterlosses.
 4. An antenna amplifier according to claim 1, furthercomprising: connected to the input and to the output of the low noiseamplifier first quarter-wavelength conductors terminated with diodesconnected to signal earth, and second quarter-wavelength conductors eachhaving a respective connection point for delivery of an input signal andthe output of an amplified signal respectively, and thirdquarter-wavelength conductors connected to said connection points andterminated with diodes connected to signal earth, wherein means areprovided for current supply to the diodes to render said diodeselectrically conductive, and a by-pass line between the two thirdquarter-wavelength conductors at their connections to respective diodes.5. An antenna amplifier according to claim 1, wherein the resonators aredisposed in a curved cavity defined by a metal casing.
 6. An antennaamplifier according to claim 5, wherein the curved cavity has ahorseshoe configuration.
 7. An antenna amplifier according to claim 1,further comprising a notch resonator provided on each end of the cavityoutwardly of the connecting pins on said ends.
 8. An antenna amplifieraccording to claim 1, wherein two comb-line filters are mounted in thehorseshoe-shaped cavity, a first filter for transmitter frequenciesfully accommodated in one leg of the horseshoe, a second for receiverfrequencies accommodated in a part of the horseshoe comprising thesecond leg and the curved part of the aperture, wherein the secondfilter has a larger number of resonators than the first filter.
 9. Anantenna amplifier for an antenna intended for transmission in a firstfrequency band and for receiving in a second frequency band which isdifferent from the first frequency band, comprising:an antennaconnection; a transceiver connection; a filter means for providing afirst frequency-separated conductor path for the first frequency bandextending from said transceiver connection to said antenna connectionand a second frequency-separated conductor path for the second frequencyband extending from said antenna connection to said transceiverconnection; said second conductor path including a low noise amplifier;said first conductor path including a first resonator-constructedbandpass filter, for the first frequency band intended for transmission,immediately connected between said transceiver connection and saidantenna connection; said second conductor path including a secondbandpass filter, said second bandpass filter comprising a first endconnected immediately to one end of said antenna connection; and a thirdbandpass filter comprising a first end immediately connected to saidtransceiver connection, said low noise amplifier having an inputconnected to a coupling or inputting element at a second end of saidsecond bandpass filter and having an output connected to a coupling orinputting element at a second end of said third bandpass filter, whereinthe pass bands of said second and third bandpass filters correspond tothe second frequency band.
 10. An antenna amplifier according to claim9, wherein said low noise amplifier input is connected to said secondend of the second bandpass filter in a contact-free and cable-freemanner.
 11. An antenna amplifier according to claim 9, wherein thefirst, second and third filters constructed with resonators are eachdisposed in a cavity having a first cavity part that accommodates thefirst bandpass filter, the antenna connection and the transceiverconnection, and a second and a third cavity part which extend generallyparallel with one another and accommodate components of the second andthe third filter and which are coupled to the antenna connection and tothe transceiver connection respectively via apertures.
 12. An antennaamplifier having an antenna connection, a transmitter input connected tothe antenna connection via a first transmitter frequency bandpassfilter, and an input to an amplifier for receiver frequencies connectedto said antenna connection via a second receiver frequency bandpassfilter, said amplifier having an output that can be connected to areceiver, wherein the bandpass filters are comb-line filters whoseresonators are accommodated in a curved cavity defined by a metalcasing, the amplifier is constructed in a circuit board in accordancewith microstrip or stripline technology and has an input adaptivelyconnected via a connecting pin embodied at right angles to the circuitboard; and a connecting pin is provided at respective ends of thecavity.
 13. An antenna amplifier according to claim 12, wherein thecurved cavity has a horseshoe configuration.
 14. An antenna amplifieraccording to claim 13, wherein three comb-line filters are arranged inthe horseshoe-shaped cavity, each with a respective bandpass filter forreceiver frequency at respective legs of the horseshoe-shape, and abandpass filter for transmitter frequency at the curved part of saidcavity, with antenna and downlead connecting pins between the comb-linefilters, and a respective connecting pin at the ends of the legs forconnection to the input and output respectively of the circuitboard-mounted amplifier.
 15. An antenna amplifier according to claim 13,wherein the connecting pins connecting the antenna and downleadrespectively are each connected to a respective coaxial connection. 16.An antenna amplifier according to claim 12, further comprising a notchresonator provided on each end of the cavity outwardly of the connectingpins on said ends.
 17. An antenna amplifier according to claim 12,wherein two comb-line filters are mounted in the horseshoe-shapedcavity, a first filter for transmitter frequencies fully accommodated inone leg of the horseshoe, a second for receiver frequencies accommodatedin a part of the horseshoe comprising the second leg and the curved partof the aperture, wherein the second filter has a larger number ofresonators than the first filter.
 18. An antenna amplifier according toclaim 12, wherein the input of the circuit board-mounted amplifier isconnected with the aid of a connecting pin whose one end is attached toa cavity wall and the other end of which is extended through a hole inan opposite cavity wall and is in contact with an impedance-adaptedcircuit board conductor on said circuit board, said connecting pinforming an inductive connection with the circuit board conductor.
 19. Anantenna amplifier according to claim 12, wherein one end of theconnecting pin is attached to a cavity wall and is connectedcapacitively with an impedance-adapted circuit board conductor on saidcircuit board, via a hole in an opposite cavity wall.